Semiconductor light emitting device and method of manufacturing the same

ABSTRACT

An n-type layer ( 3 ) and a p-type layer ( 5 ) which are made of a gallium nitride based compound semiconductor are provided on a substrate ( 1 ) so that a light emitting layer forming portion ( 10 ) for forming a light emitting layer is provided. A gallium nitride based compound semiconductor layer containing oxygen is used for at least one layer of the light emitting layer forming portion ( 10 ). In the case where a buffer layer ( 2 ) made of the gallium nitride based compound semiconductor or aluminum nitride is provided between the substrate ( 1 ) and the light emitting layer forming portion ( 10 ), the buffer layer ( 2 ) and/or at least one layer of the light emitting layer forming portion ( 10 ) may contain oxygen. By such a structure, crystal defects of the semiconductor layer of the light emitting layer forming portion ( 10 ) can be decreased and a luminance can highly be enhanced. Thus, it is possible to obtain a blue color type semiconductor light emitting device having a high luminance.

TECHNICAL FIELD

The present invention relates to a semiconductor light emitting devicein which a gallium nitride based compound semiconductor layer isprovided on a substrate, thereby forming a light emitting diode and asemiconductor laser diode. More particularly, the present inventionrelates to a semiconductor light emitting device capable of reducing theinfluence of a shift of a crystal lattice between the substrate and thegallium nitride based compound semiconductor, thereby enhancing lightemitting characteristics.

BACKGROUND ART

Conventionally, a semiconductor light emitting device using a galliumnitride based compound semiconductor for emitting blue color type light(yellow from ultraviolet rays), for example, has had a structure shownin FIG. 7. More specifically, the semiconductor light emitting devicecomprises a low-temperature buffer layer 22 made of GaN on a sapphiresubstrate 21, for example, an n-type layer (a clad layer) 23 in whichn-type GaN is epitaxially grown at a high temperature, an active layer24 formed of a compound semiconductor made of a material for defining alight emitting wavelength to have a smaller band gap energy than theband gap energy of the clad layer, for example, an InGaN based compoundsemiconductor (which means that a ratio of In to Ga can be variouslychanged and so is the following), and a p-type layer (a clad layer) 25including a p-type AlGaN based compound semiconductor layer 25 a (whichmeans that a ratio of Al to Ga can be variously changed and so is thefollowing) and a GaN layer 25 b, and a p-side electrode 28 is providedon the surface of the GaN layer 25 b and an n-side electrode 29 isprovided on the surface of the n-type layer 23 which is exposed byetching a part of the provided semiconductor layers. In some cases, theAlGaN based compound semiconductor layer is used on the active layer 23side of the n-type layer 23 in the same manner as the p-type layer 25 inorder to enhance the confinement effects of a carrier.

As described above, the conventional blue color type semiconductor lightemitting device using the gallium nitride based compound semiconductoris formed by providing gallium nitride based compound semiconductorssuch as GaN, InGaN based and AlGaN based compound semiconductors whichform a light emitting layer on the sapphire substrate. However, thelattice constant of the sapphire substrate is different from that of thegallium nitride based compound semiconductor by about 16%. Therefore, itis impossible to obtain a gallium nitride based compound semiconductorlayer having excellent crystalline properties. In order to solve thisproblem, a buffer layer such as GaN, AlN or the like which is formed ata low temperature is provided between a single crystal layer of thegallium nitride based compound semiconductor forming a light emittinglayer and a substrate, thereby enhancing the crystalline properties ofthe gallium nitride based compound semiconductor layer as describedabove.

Although the crystalline properties of the light emitting layer can beimproved and the blue color type semiconductor light emitting device canbe utilized by providing the above-mentioned buffer layer to be formedat a low temperature, the problem of the crystal defect of the galliumnitride based compound semiconductor layer has not completely beensolved. There has been a problem in that a luminance cannot fully beenhanced due to a great leakage current and yield cannot be enhanced dueto an insufficient luminance obtained by a slight change in amanufacturing process.

In order to solve the above-mentioned problems, it is an object of thepresent invention to provide a semiconductor light emitting devicehaving gallium nitride based compound semiconductor layers provided inwhich crystal defects based on a difference in a lattice constant can bedecreased, a leakage current can be reduced and an excellent lightemitting efficiency can be obtained.

It is another object of the present invention to provide a method formanufacturing a semiconductor light emitting device in which the crystaldefects can be decreased based on the difference in the lattice constantwhen the gallium nitride based compound semiconductor layers are to beprovided.

DISCLOSURE OF THE INVENTION

The present inventors made various investigations in order to decreasecrystal defects of semiconductor layers to reduce a leakage current andto enhance a luminance when a light emitting layer forming portion madeof gallium nitride based compound semiconductor layers is to beprovided. As a result, it has been found that at least one of thegallium nitride based compound semiconductor layers constituting thelight emitting layer forming portion is caused to contain oxygen,thereby decreasing a crystal defect density and enhancing a luminance.Moreover, the following has been found. In the case were onesemiconductor layer is caused to contain oxygen, it is provided on theunderside as much as possible, thereby decreasing the crystal defects ofthe semiconductor layer provided thereon to enhance a luminance. In thecase where a buffer layer made of a gallium nitride based compoundsemiconductor is provided between the substrate and the light emittinglayer forming portion, the crystal defects of the semiconductor layerprovided on the buffer layer can be improved even if the buffer layercontains oxygen. Furthermore, it has been found that in the case wherethe buffer layer is made of AlN, the crystalline properties can beimproved even if the AlN is caused to contain oxygen and can be improvedstill more by causing a plurality of layers to contain oxygen.

The present invention provides a semiconductor light emitting devicecomprising a substrate, a buffer layer provided on the substrate andmade of a gallium nitride based compound semiconductor, and a lightemitting layer forming portion in which a gallium nitride based compoundsemiconductor including an n-type layer and a p-type layer to form alight emitting layer is provided on the buffer layer, wherein the bufferlayer or at least one of semiconductor layers constituting the lightemitting layer forming portion is a compound semiconductor whichcontains oxygen in a gallium nitride based compound.

The gallium nitride based compound semiconductor means a semiconductormade of a compound of III group element Ga and V group element N, or acompound obtained by substituting a part of the III group element Ga foranother III group element such as Al, In or the like and/or bysubstituting all or a part of the V group element N for another V groupelement such as P, As or the like.

The compound semiconductor containing the oxygen is made ofGa_(1−x−y)Al_(x)In_(y)O_(z)N_(1−z) (0≦x<1, 0≦y<1, 0<z<1). The compoundsemiconductor containing the oxygen may contain an n-type impurityand/or a p-type impurity. The n-type impurity means at least one kind ofSi, Se, Te and the like, and the p-type impurity means at least one kindof Mg, Zn, Be and the like.

Furthermore, the compound semiconductor containing the oxygen is usedfor the buffer layer, is used for a semiconductor layer on at least thebuffer layer side of the light emitting layer forming portion, is usedfor the active layer interposed between the n-type layer and the p-typelayer constituting the light emitting layer forming portion, or is usedfor two layers or more such as the buffer layer and the semiconductorlayer of the light emitting layer forming portion which is in contactwith the buffer layer.

More specifically, the substrate is made of a sapphire substrate and thebuffer layer is made of GaO_(z)N_(1−z) (0<z<1), and more specifically,the light emitting layer forming portion has a double heterojunctionstructure in which the active layer is interposed between an n-typesemiconductor layer and a p-type semiconductor layer, and asemiconductor layer which is in contact with at least the buffer layerof the light emitting layer forming portion is made of a GaO_(z)N_(1−z)(0<z<1) single crystal layer.

The buffer layer can contain at least one kind selected from a groupincluding Si, Se, Te, Mg, Zn and Be.

According to the semiconductor light emitting device of the presentinvention, irrespective of the presence or not of the buffer layer and amaterial thereof, a gallium nitride based compound semiconductorincluding an n-type layer and a p-type layer to form a light emittinglayer is provided on a substrate, thereby providing a light emittinglayer forming portion, wherein at least one of semiconductor layersconstituting the light emitting layer forming portion is formed by acompound semiconductor layer containing oxygen in a gallium nitridebased compound. Consequently, the crystal defects of the semiconductorlayer can be decreased, thereby enhancing a luminance.

A buffer layer made of AlN may be provided between the substrate and thelight emitting layer forming portion and a buffer layer made ofAlO_(u)N_(1−u) (0<u<1) may be provided between the substrate and thelight emitting layer forming portion.

Furthermore, the semiconductor light emitting device according to thepresent invention comprising a substrate, a buffer layer made ofAlO_(u)N_(1−u) (0<u<1) provided on the substrate, and a light emittinglayer forming portion in which a gallium nitride based compoundsemiconductor including an n-type layer and a p-type layer to form alight emitting layer is provided on the buffer layer.

A part of Al of the buffer layer may be substituted for In, and thebuffer layer may contain at least one kind selected from a groupincluding Si, Se, Te, Mg, Zn and Be.

In the case where at least one of the semiconductor layers constitutingthe light emitting layer forming portion is made ofGa_(1−x−y)Al_(x)In_(y)O_(z)N_(1−z) (0≦x<1, 0≦y<1, 0<z<1), a luminancecan be enhanced still more. More specifically, the substrate is formedof a sapphire substrate, and the light emitting layer forming portionhas a double heterojunction structure in which an active layer isinterposed between the n-type layer and the p-type layer.

The present invention provides a method of manufacturing a semiconductorlight emitting device comprising the steps of providing a buffer layermade of a gallium nitride based compound semiconductor on a substrate ata low temperature by the Metal Organic Vapor Phased Epitaxy (MOVPE)method, the (Hydride Vapor Phased Epitaxy (HVPE) method or the MolecularBeam Epitaxy (MBE) method, sequentially providing semiconductor layersconstituting a light emitting layer forming portion made of a galliumnitride based compound semiconductor at a high temperature, andsupplying or while supplying an oxidizing source when growing the bufferlayer and/or at least one of the semiconductor layers constituting thelight emitting layer forming portion.

The oxidizing source can supply oxygen, ozone, N₂O, H₂O and the like,and can liberate oxygen of oxide in a growing furnace such as a chambermade of a quartz glass.

As another manufacturing method, the present invention provides a methodof manufacturing a semiconductor light emitting device comprising thesteps of providing a buffer layer made of AlO_(u)N_(1−u) (0<u<1) onto asubstrate at a low temperature by the MOVPE method, the HVPE method orthe MBE method by supplying or while supplying an oxidizing source, andsequentially epitaxially growing semiconductor layers constituting alight emitting layer forming portion made of a gallium nitride basedcompound semiconductor at a high temperature. In this case, theoxidizing source may be supplied when forming at least one layer of thelight emitting layer forming portion or performing growth whilesupplying the oxidizing source and growing a semiconductor layer made ofGa_(1−x−y)Al_(x)In_(y)O_(z)N_(1−z) (0≦x<1, 0≦y<1, 0<z<1).

The oxidizing source may be supplied by introducing the oxidizing sourceinto a growing furnace for growing the semiconductor layer or by usingoxygen of oxide in the growing furnace for growing the semiconductorlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a semiconductor light emitting deviceaccording to an embodiment of the present invention;

FIG. 2 is a chart showing a crystal defect density of an n-type layerobtained by changing an amount z of GaO_(z)N_(1−z) of the n-type layerin FIG. 1 and a change in a luminance of the light emitting device;

FIG. 3 is a chart showing a voltage at a predetermined leakage currentobtained by changing the amount z of GaO_(z)N_(1−z) of the n-type layerwith the structure in FIG. 1, the voltage is obtained when a currentvalue becomes to the predetermined value when the voltage is increased;

FIG. 4 is a chart showing a change in a crystal defect density of then-type layer obtained by changing the amount z of GaO_(z)N_(1−z) for abuffer layer and a change in a luminance of the light emitting device;

FIG. 5 is a chart showing a voltage at a predetermined leakage currentobtained by changing the amount z of GaO_(z)N_(1−z) to be used for thebuffer layer, the voltage is obtained when a current value becomes thepredetermined value when the voltage is increased;

FIG. 6 is a voltage to current characteristic chart showing a risingportion which is obtained when a voltage is applied, for explaining aleakage current of the semiconductor light emitting device; and

FIG. 7 is a perspective view showing an example of a semiconductor lightemitting device using a gallium nitride based compound semiconductoraccording to the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

A semiconductor light emitting device according to the present inventioncomprises a buffer layer 2 made of a gallium nitride based compoundsemiconductor provided on the surface of a substrate 1 made of sapphire(an Al₂O₃ single crystal), for example, and a light emitting layerforming portion 10 in which gallium nitride based compound semiconductorlayers including an n-type layer 3 and a p-type layer 5 to form a lightemitting layer is provided on the buffer layer 2 as shown in a sectionalview illustrating an embodiment in FIG. 1, for example. An example shownin FIG. 1 is characterized in that a semiconductor layer of the n-typelayer 3 constituting the light emitting layer forming portion 10 isformed of a compound semiconductor containing oxygen in a galliumnitride based compound.

In the example shown in FIG. 1, the semiconductor layers provided on thesapphire substrate 1 have a structure in which a low-temperature bufferlayer 2 made of GaN is deposited in a thickness of about 0.01 to 0.2 μmat a low temperature of about 500° C., an n-type layer (clad layer) 3made of n-type GaO_(z)N_(1−z) which has a thickness of about 1 to 5 μmat a high temperature of about 1000° C., an active layer 4 made of anon-doped InGaN based compound semiconductor which has a thickness ofabout 0.002 to 0.3 μm (if blue light is to be emitted, In has a rate of0.3 to 0.5 and Ga has a rate of 0.7 to 0.5 with non-doping, and Si andZn can be doped to cause the In to have a rate of about 0.05, therebyperforming impurity light emission), and a p-type layer 5 having ap-type AlGaN based compound semiconductor layer 5 a and a GaN layer 5 bprovided in a thickness of about 0.05 to 0.5 μm are sequentially grown,thereby providing a light emitting layer forming portion 10. A p-sideelectrode 8 is formed on the surface of the provided semiconductorlayers through a current diffusion layer 7 made of an alloy layer of Niand Au and having a thickness of about 2 to 100 nm, for example, and ann-type electrode 9 is formed on the n-type layer 3 exposed by removing apart of the provided semiconductor layers 3 to 5.

It is preferable that the rate of 0 of GaOzN1−z of the above-mentionedn-type layer 3, that is, the range of z should be 0.2 or more as will bedescribed below. However, even if the range of z is 0.1, remarkableeffects can be obtained. Therefore, the small range can be applied andthe rate can be selected in the range of 0<z<1 based on the relationshipwith other layers.

In the example shown in FIG. 1, the p-type layer 5 is formed of a doublelayer having the GaN layer 5 b and the AlGaN based compoundsemiconductor layer 5 a because it is preferable that a layer containingAl should be provided on the active layer 4 side in respect of theconfinement effect of a carrier and only the GaN layer may be provided.Moreover, the AlGaN based compound semiconductor layer may be providedon the n-type layer 3 to form a double layer, and these can also beformed of other gallium nitride based compound semiconductor layers.Furthermore, while the buffer layer 2 is also formed of the GaN layer,it may be formed of other semiconductor layers such as an AlN layer, anAlGaN based compound semiconductor layer, a layer to which In is addedand the like.

Next, an enhancement in the luminance of the semiconductor lightemitting device having the structure shown in FIG. 1 will be describedbelow. As described above, the present inventors variously investigatedto decrease, as much as possible, lattice defects generated on thegallium nitride based compound semiconductor layer constituting thelight emitting layer forming portion provided on the sapphire substrate,thereby enhancing the luminance, for example. As a result, it has beenfound that the gallium nitride based compound semiconductor layerprovided on the substrate containing oxygen, thereby greatly reducing acrystal defect density and highly enhancing the luminance.

More specifically, in the blue color type semiconductor light emittingdevice with the structure shown in FIG. 1, a change in a crystal defectdensity on the surface of the n-type layer 3 which is obtained bychanging the amount (z) of oxygen of the n-type layer 3 made ofGaO_(z)N_(1−z) and a change in the luminance obtained in the state ofthe light emitting device were checked. As a result, when the oxygen wascontained at a rate of z of about 0.1, the crystal defect density andthe luminance were greatly enhanced. When z has a value of 0.2 or more,the crystal defect density was enhanced by about 2 orders and theluminance was enhanced by three times or more as shown in FIG. 2. InFIG. 2, A denotes a crystal defect density and B denotes a luminance.The n-type layer 3 had a thickness of 5 μm, the buffer layer 2 was madeof GaN in a thickness of about 0.03 μm, the active layer 4 was made ofIn_(0.05)Ga_(0.95)N doped with Si and Zn in a thickness of about 0.2 μm,and the p-type layer 5 had a lamination structure including theAl_(0.15)Ga_(0.85)N layer 5 a in a thickness of 0.2 μm and the GaN layer5 b in a thickness of about 0.3 μm, and only the value of z was changedfor manufacture. The crystal defect density was measured by an etch pitmethod for measuring the number of pits which are dents generated byetching the surface of the provided n-type layer 3 without providing asemiconductor layer such as a next active layer. A luminance wasmeasured in the state in which the n-type layer 3 was provided and theactive layer 4, the p-type layer 5 and the like were continuouslyprovided to make a semiconductor light emitting device, and is a resultof the relative luminance obtained by setting a luminance to 1 when theconventional n-type layer is made of GaN.

This phenomenon in which less crystal defects are generated could alsobe confirmed by measuring a leakage current of the semiconductor lightemitting device. More specifically, the characteristic of a voltage (V)and a current (log I (logarithmic scale)) of the semiconductor lightemitting device is generally identical to the characteristic shown by Cof FIG. 6. Even if the voltage of the V−log I characteristic is raised,the current is saturated and is not increased. It becomes almostconstant by depending on the resistance of the contact portion ofelectrodes. However, the V−log I characteristic of the semiconductorlight emitting device having a great leakage current rises quickly asshown by D. For this reason, it is apparent that a lower voltage (acurve D indicative of V1has a greater leakage current by measuringvoltage V1 and V2 with a constant current value (for example, 1 μA) logI1. As shown in FIG. 3, a voltage is plotted with a constant current byusing z of the above-mentioned GaO_(z)N_(1−z) as a parameter. It is alsoapparent from FIG. 3 that oxygen is contained to generate a smallerleakage current (a high voltage with a constant current) than the GaNlayer having z of 0.

As is apparent from FIGS. 2 and 3, the n-type layer 3 contains oxygen sothat the number of crystal defects is greatly decreased and a luminanceis also enhanced. The GaO_(z)N_(1−z) is dominantly grown more quickly ina transverse direction than in a vertical direction as compared with theGaN. Therefore, it is believed that a film having less defects can begrown because the film is connected in the transverse direction andbecomes a flat film and is grown in the vertical direction. When a flatfilm having less defects is formed, a film grown thereon also has lessdefects and is flat. Therefore, flat films having less defects areformed for the active layer and the p-type layer. Thus, a semiconductorlight emitting device having a high luminance can be obtained. For thisreason, it is guessed that in the case where the oxygen is to be addedto only one layer, the oxygen is preferably added as lower as possible(to the side closer to the substrate).

From this viewpoint, the state of the crystal defect of the n-type layerand the change of the luminance were similarly investigated by causingthe buffer layer 2 formed at a low temperature to contain oxygen inplace of the n-type layer epitaxially grown at a high temperature. Morespecifically, a film having a thickness of about 0.03 μm was formed at atemperature of about 500° C. by using GaO_(z)N_(1−z) for the bufferlayer 2, by variously changing the value of z of the buffer layer 2, then-type layer 3 was formed of n-type GaN in a thickness of about 5 μm,and the active layer 4 and the p-type layer 5 were in the same manner asthe above-mentioned example. The density of the crystal defect and theluminance of the light emitting device were checked by using theGaO_(z)N_(1−z) for the buffer layer 2. The result of the checking isshown in FIG. 4. Also in FIG. 4, A denotes a crystal defect density andB denotes a luminance. The crystal defect density was obtained by anetch pit method in which the n-type layer 3 is epitaxially grown on thebuffer layer 2 and is etched in the same manner as the foregoing,thereby checking the number of pits. The luminance was checked with arelative value on the basis of a luminance obtained by using the GaN forthe buffer layer in the state in which the light emitting device is madeas described above. In the same manner as the foregoing, FIG. 5 showsthe relationship of a voltage obtained with a constant currentindicative of a leakage current in the light emitting device.

As is apparent from FIGS. 4 and 5, the crystal defect density isdecreased and the luminance is also enhanced by using the GaO_(z)N_(1−z)having oxygen added thereto for the buffer layer, although thecrystalline properties are lowered than the case where theGaO_(z)N_(1−z) is used for the above-mentioned n-type layer. However,the present structure is clearly more enhanced than the conventionalstructure. This can be considered as follows. More specifically, sincethe buffer layer 2 is grown at a low temperature, it is believed thatthe buffer layer 2 does not become a single crystal during growth but isset in an amorphous state, so a layer having less crystal defects with adense film such as the single crystal layer of the GaO_(z)N_(1−z) isobtained with difficulty even if the buffer layer 2 contains oxygen.However, at least the surface of the buffer layer 2 is changed into asingle crystal during the growth of the next n-type layer 3 at a hightemperature. Since the single crystal layer contains oxygen, it is adense layer having less crystal defects and a single crystal layer to beformed thereon is also provided in alignment with the layer having lesscrystal defects on the surface of the buffer layer. Consequently, it isbelieved that a semiconductor layer having less crystal defects can beobtained. As a result, a gallium nitride based compound semiconductorcontaining oxygen can be used for the buffer layer. Consequently, evenif a semiconductor layer to be provided on the buffer layer is a galliumnitride based compound semiconductor layer containing no oxygen, asemiconductor light emitting device having less crystal defects and ahigh luminance can be obtained.

As a matter of course, the gallium nitride based compound semiconductorcontaining oxygen is used for both the buffer layer and thesemiconductor layer of the light emitting layer forming portion.Consequently, the crystal defects can be decreased still more and theluminance can be enhanced. Furthermore, the luminance could be enhancedstill more by adding oxygen to the active layer of the light emittinglayer forming portion having the above-mentioned structure.

The present inventors also investigated crystalline properties obtainedin the case where an oxidizing source is supplied to form an AlN filmwith a composition of AlO_(u)N_(1−u) (0<u<1) containing oxygen when AlNis to be used for the buffer layer. In this case, the light emittinglayer forming portion 10 had the same structure as in the case whereGaO_(z)N_(1−z) is used for the above-mentioned buffer layer 2. Thebuffer layer 2 was formed in a thickness of about 0.03 μm at a lowtemperature of about 500° C. Also in this case, the defect density waslowered by about two orders with the rate of the oxygen to be containedin the same manner as in the case where the above-mentionedGaO_(z)N_(1−z) was used for the buffer layer 2, that is, a value of u ofabout 0.2 and the luminance was remarkably increased, thereby it issupposed to obtain the same effects with other values of u. In the samemanner as in the above-mentioned GaO_(z)N_(1−z), since the buffer layer2 is grown at a low temperature, it does not become a single crystalduring the growth but is set in an amorphous state of AlO_(u)N_(1−u) Itis supposed that a layer having less crystal defects with a dense filmsuch as a single crystal layer can be obtained with difficulty. However,it is supposed that at least the surface of the buffer layer 2 ischanged into a single crystal and becomes dense during the growth of thenext n-type layer 3 at a high temperature and a semiconductor layerhaving less crystal defects is provided as described above. As a result,the AlO_(u)N_(1−u) containing oxygen is used for the buffer layer 2.Consequently, a gallium nitride based compound semiconductor layerprovided on the buffer layer 2 has less crystal defects. Thus, asemiconductor light emitting device having a high luminance can beobtained. It is preferable that the thickness of the buffer layer 2should be 0.01 to 0.2 μm in the same manner as the foregoing in order toget the buffer function.

In order to obtain the gallium nitride based compound semiconductorlayer having less crystal defects by flattening the surface of thesapphire substrate, there has been known a method in which the surfaceof the sapphire substrate is nitrided to obtain Al₂ (ON)₃ and alow-temperature buffer layer made of GaN is formed on the Al₂ (ON)₃ anda gallium nitride based compound semiconductor is provided on the bufferlayer. Also in this case, however, the surface of the sapphire substrateis nitrided to make Al₂ (ON)₃ and the buffer layer is a GaN layer grownat a low temperature. Even if the surface of the sapphire substrate isflattened, a dense film is not formed in the same manner as the directformation of the GaN layer on the sapphire substrate. In addition, thegallium nitride based compound semiconductor layer grown on the GaNlayer at a high temperature is not changed into a dense film as in thepresent invention.

Next, a method for manufacturing a semiconductor light emitting deviceshown in FIG. 1 will be described below.

By the MOVPE method, a reaction gas such as trimethyl gallium (TMG),ammonia (NH₃) or the like is supplied together with a carrier gas H₂.First of all, a low-temperature buffer layer 2 made of a GaN layer isformed on a sapphire substrate 1 in a thickness of about 0.01 to 0.2 μmat a temperature of about 400 to 600° C. for example.

Then, SiH₄ or the like acting as an n-type dopant gas, and furthermore,O₂ acting as an oxidizing source are added to the above-mentionedreaction gas at a high temperature of about 600 to 1200° C., forexample, and an n-type layer 3 made of n-type GaO_(z)N_(1−z) is grown ina thickness of about 1 to 5 μm. Thereafter, trimethyl indium(hereinafter referred to as TMIn) is added to the reaction gas, dimethylzinc (DMZn) is further added to the SiH₄ of the dopant gas, and theactive layer 4 made of an InGaN based compound semiconductor doped withSi and Zn is formed in a thickness of about 0.002 to 0.3 μm.Subsequently, trimethyl aluminum (hereinafter referred to as TMA) isintroduced in place of the TMIn, and cyclopentadienyl magnesium (Cp₂Mg)or dimethyl zinc (DMZn) are further used as the dopant gas, therebygrowing a p-type AlGaN based compound semiconductor layer 5 a in athickness of about 0.05 to 0.5 μm, then stopping the introduction of theTMA to grow p-type GaN in a thickness of about 0.05 to 0.5 μm, andforming the p-type layer 5 in a thickness of about 0.1 to 1 μm as awhole.

Then, for example, Ni and Au are provided by vacuum deposition or thelike and is sintered and alloyed. Consequently, a current diffusionlayer 7 is formed in a thickness of about 2 to 100 nm. Thereafter, aresist film is provided on a surface and is patterned. A part of thelaminated semiconductor layers is removed by reactive ion etching usinga chlorine gas or the like, thereby exposing the n-type layer 3. By thelift off method, for example, Ti and Al are provided and sintered to beelectrically connected to the n-type layer 3 by the lift off method.Consequently, an n-side electrode 9 made of an alloy layer of bothmetals is formed. For example, similary, Ti and Au are provided to beelectrically connected to the p-type layer 5. Thus, a p-side electrode 8having a lamination structure of both metals is formed. As a result, thesemiconductor light emitting device shown in FIG. 1 can be obtained.

While the semiconductor layer has been grown by the MOVPE method in thisexample, the same semiconductor layer can also be grown by the HVPEmethod or the MBE method. Although O₂ has been used for the oxidizingsource, it is not restricted thereto but a material capable ofperforming oxidation can be used. Accordingly, it is also possible toutilize oxygen liberated from oxide such as N₂O, H₂O or a quartz glassin a growing furnace or oxygen which can be liberated by introducing areducing agent, and the like.

Although the GaN layer has been used for the gallium nitride basedcompound semiconductor layer to be contained oxygen in each of theabove-mentioned examples, the same results could be obtained by using amixed crystal gallium nitride based compound semiconductor to whichanother III group element is added, for example, an AlGaN based compoundsemiconductor layer, an InGaN based compound semiconductor layer or thelike.

Furthermore, while the buffer layer has been formed with non-doping inthe above-mentioned example, an n-type impurity such as Si, Se, Te orthe like may be introduced to obtain an n-type or a p-type impurity suchas Mg, Zn, Be or the like may be introduced to obtain a p-type, therebygrowing the p-type layer of the light emitting layer forming portionearlier. Moreover, while the n-type layer of the light emitting layerforming portion contains oxygen in the above-mentioned example, thep-type layer and the non-doped layer may contain the oxygen. Inparticular, in the structure in which the p-type layer is formed on thesubstrate side, the active layer and the n-type layer are provided onthe p-type layer so that the light emitting layer forming portion isprovided, it is preferable that the p-type layer should contain oxygenin such a manner that the p-type layer is a lower layer. In brief, thepresent invention can be applied to the compound semiconductor layercontaining Ga and N.

Although GaN, GaO_(z)N_(1−z) and AlO_(z)N_(1−z) have been used for thebuffer layer in the example, effects can be obtained even if the bufferlayer has another composition such as AlN when the gallium nitride basedcompound semiconductor containing oxygen is used for the light emittinglayer forming portion. Also in the case where AlO_(z)N_(1−z) is used forthe buffer layer, the same effects can be obtained with a structure inwhich a part of Al is substituted for another III group element such asIn and a structure in which the above-mentioned n-type impurity and/orp-type impurity are is added.

Furthermore, while the sapphire substrate has been used for thesubstrate in the above-mentioned example, the sapphire substrate is notrestricted but the present invention can be applied to the case wherethe gallium nitride based compound semiconductor is provided on othersemiconductor substrates such as a SiC substrate, a Si substrate, a GaAssubstrate and the like.

Although the active layer has been formed by Si an Zn doping in each ofthe above-mentioned examples, it may be formed by non-doping.Furthermore, while there has been an example of a double heterojunctionstructure in which the active layer is interposed between the n-typelayer and the p-type layer as the light emitting layer forming portion,the same effects can be obtained with a pn junction structure in whichthe n-type layer and the p-type layer are directly joined.

According to the present invention, also in the case where the galliumnitride based compound semiconductor layer is grown on a substratehaving different lattice constants, the crystalline properties of thesemiconductor layer in the light emitting layer forming portion aregreatly be enhanced because at least one of the gallium nitride basedcompound semiconductor layers and/or the GaN based or AlN based compoundsemiconductor of the buffer layer contain(s) oxygen. As a result, aluminance is increased, and a variation is reduced in respect ofmanufacture. Thus, it is possible to obtain an inexpensive blue colortype semiconductor light emitting device having a high luminance.

INDUSTRIAL APPLICABILITY

According to the semiconductor light emitting device of the presentinvention, blue color (B) type light having a high luminance can beobtained and can be utilized as various blue color type light sources,and is used together with red color (R) and green color (G) lightemitting devices, thereby obtaining light sources having any mixedcolor. Thus, the semiconductor light emitting device can be utilized ina variety of fields such as a traffic light, a display unit such as alarge-sized display and the like.

What is claimed is:
 1. A semiconductor light emitting device comprising:a substrate; a buffer layer provided on said substrate and made of agallium nitride based compound semiconductor; and a light emitting layerforming portion in which gallium nitride based compound semiconductorlayers including an n-type layer and a p-type layer to form a lightemitting layer are provided on said buffer layer; wherein at least oneof said buffer layer and said semiconductor layers constituting saidlight emitting layer forming portion is a compound semiconductor whichcontains oxygen as an element constituting the compound in a galliumnitride based compound.
 2. The semiconductor light emitting device ofclaim 1, wherein said compound semiconductor containing oxygen is madeof Ga_(1−x−y)Al_(x)In_(y)O_(z)N_(1−z) (0≦x<1, 0≦y<1, 0<z<1).
 3. Thesemiconductor light emitting device of claim 2, wherein said compoundsemiconductor containing oxygen contains at least one of an n-typeimpurity and a p-type impurity.
 4. The semiconductor light emittingdevice of claim 1, wherein said compound semiconductor containing oxygenis used for said buffer layer.
 5. The semiconductor light emittingdevice of claim 1, wherein said compound semiconductor containing oxygenis used for a semiconductor layer on at least a buffer layer side ofsaid light emitting layer forming portion.
 6. The semiconductor lightemitting device of claim 1, wherein said light emitting layer formingportion has a double heterojunction structure in which an active layeris interposed between said n-type layer and said p-type layer, and saidcompound semiconductor containing oxygen is used for said active layer.7. The semiconductor light emitting device of claim 4, wherein saidsubstrate is made of a sapphire substrate and said buffer layer is madeof GaO_(z)N_(1−z) (0<z<1).
 8. The semiconductor light emitting device ofclaim 7, wherein said buffer layer contains at least one kind selectedfrom a group including Si, Se, Te, Mg, Zn and Be.
 9. The semiconductorlight emitting device of claim 5, wherein said light emitting layerforming portion has a double heterojunction structure in which an activelayer is interposed between said n-type semiconductor layer and saidp-type semiconductor layer, and a semiconductor layer which is incontact with at least said buffer layer of said light emitting layerforming portion is made of a GaO_(z)N_(1−z) (0<z<1) single crystallayer.
 10. A semiconductor light emitting device comprising: asubstrate; a light emitting layer forming portion in which galliumnitride based compound semiconductor layers including an n-type layerand a p-type layer to form a light emitting layer are provided on saidsubstrate; wherein at least one of said semiconductor layersconstituting said light emitting layer forming portion is a compoundsemiconductor layer which contains oxygen in a gallium nitride basedcompound.
 11. The semiconductor light emitting device of claim 10,wherein a buffer layer made of AlN is provided between said substrateand said light emitting layer forming portion.
 12. The semiconductorlight emitting device of claim 10, wherein a buffer layer made ofAlO_(u)N_(1−u) (0<u<1) is provided between said substrate and said lightemitting layer forming portion.
 13. A semiconductor light emittingdevice comprising: a substrate; a buffer layer made of AlO_(u)N_(1−u)(0<u<1) provided on said substrate; and a light emitting layer formingportion in which gallium nitride based compound semiconductor layersincluding an n-type layer and a p-type layer to form a light emittinglayer is provided on said buffer layer.
 14. The semiconductor lightemitting device of claim 13, wherein said buffer layer further comprisesin.
 15. The semiconductor light emitting device of claim 13, whereinsaid buffer layer contains at least one kind selected from a groupincluding Si, Se, Te, Mg, Zn and Be.
 16. The semiconductor lightemitting device of claim 13, wherein at least one of said semiconductorlayers constituting said light emitting layer forming portion is made ofGa_(1−x−y)Al_(x)In_(y)O_(z)N_(1−z) (0≦x<1, 0≦y<1, 0<z<1).
 17. Thesemiconductor light emitting device of claim 16, wherein said substrateis formed of a sapphire substrate, and said light emitting layer formingportion has a double heterojunction structure in which an active layeris interposed between said n-type layer and said p-type layer.
 18. Amethod of manufacturing a semiconductor light emitting device comprisingthe steps of: providing a buffer layer made of a gallium nitride basedcompound semiconductor on a substrate by the MOVPE method, the HVPEmethod or the MBE method; sequentially providing semiconductor layersconstituting a light emitting layer forming portion made of a galliumnitride based compound semiconductor; and supplying or while supplyingan oxidizing source when growing a semiconductor layer containing oxygenas an element constituting compound, said semiconductor layer being atleast one of said buffer layer and said semiconductor layersconstituting said light emitting layer forming portion.
 19. A method ofmanufacturing a semiconductor light emitting device comprising the stepsof: providing a buffer layer made of AlO_(u)N_(1−U) (0<u<1) onto asubstrate by the MOVPE method, the HVPE method or the MBE method bysupplying or while supplying an oxidizing source; and sequentiallyepitaxially growing semiconductor layers constituting a light emittinglayer forming portion made of a gallium nitride based compoundsemiconductor.
 20. The manufacturing method of claim 19, wherein growingat least one layer of said light emitting layer forming portion bysupplying or while supplying an oxidizing source and growing asemiconductor layer made of Ga_(1−x−y)Al_(x)In_(y)O_(z)N_(1−z) (0≦x<1,0≦y<1, 0<z<1).
 21. The manufacturing method of claim 18, wherein saidoxidizing source is supplied by introducing the oxidizing source into agrowing furnace for growing said buffer layer or said semiconductorlayers.
 22. The manufacturing method of claim 18, wherein said oxidizingsource is supplied by an oxide in a growing furnace for growing saidbuffer layer or said semiconductor layers.